The
Towers of Backbone.

The enigma of Backbone has been with us for over 30 years since Peter Laurie
first referred to the use of microwave relay towers in his 1967 Sunday Times article
on civil defence. Three years later he expanded the article into the groundbreaking
“Beneath The City Streets”
in which he says “The GPO planned a chain of concrete towers code-named
Backbone which linked the 3 major cities, as well as having connections with the
air-defence chain”. Unfortunately, whilst mentioning a role for Backbone
in both civil defence and air defence he assumed that the system linked “secret
sites”, a belief founded on the mistaken, but perhaps understandable assumption
that the civil defence sites the government said it would provide existed but
because they could not be seen they must be secret. Unfortunately, we now know
they they could not be seen because they did not actually exist. Later editions
of the book largely dropped the idea of Backbone as part of a communications network
for “secret sites” but continued to maintain, correctly, that it had
some military function.

Writing some 10 years later Duncan Campbell gave us some more details in “War
Plan UK” saying that Backbone had been conceived in 1954 for a wartime
role but with a peacetime one of feeding international communications into the
US listening base at Menwith Hill. Both authors mentioned that microwave systems
like Backbone would be less vulnerable than cables to sabotage. With this thought
in mind it is interesting to note a suggestion made in a book called “Roland
Perry – the Fifth Man” which speculates that Baron Rothschild was
the fifth man in the Cambridge spy ring. This book suggested that in the early
1960s the Russians funded a string of petrol stations in Britain under the name
Nafta which were sited in out of the way places where they could be used as sabotage
bases to destroy amongst other things the Backbone stations. This is perhaps not
as far fetched as a recent suggestion that the Backbone masts were sited to coincide
with “ley lines”.

Photo: Hunters
Stones

There were some early mentions in public documents of Backbone although these
were often vague and it is perhaps only with the benefit of hindsight that we
recognise their true subject. The first public mention of what we know as Backbone
came in the 1955 Defence White Paper which announced “The Post Office…are
planning to build up a special network, both by cable and radio designed to maintain
long distance communication in the event of an attack”.

1. For younger readers, The General Post Office
the predecessor of both BT and whatever the post office is calling itself today.

An article in the October 1956 edition of the Post Office Electrical Engineer’s
Journal (POEEJ) gave a surprising amount of technical detail about Backbone although
again without being very specific -

The first use of microwave systems by the Post Office was for the transmission
of television programs; the Sutton Coldfield station of the B.B.C. was initially
linked to London by a radio-relay chain in 1949, and the Kirk O'Shotts station
has been served by a system from Manchester since 1952. …The first embodiment
of a system designed to the new Post Office specifications will be a main radio
link between London and Scotland with branches at intermediate points. The main
link will carry six broad-band channels in each direction; one or two of the broad-band
channels would be for use as a standby. Following hard on the heels of the above
“backbone” system will be the development of radio-relay systems for
up to 2,000 telephone channels, or about 1,000 telephone channels together with
one television channel.

As we will see later this article describes the system we know as Backbone
but no purpose is given for the system but it hints that a functional justification
for the microwave system was to provide the additional bandwidth required for
television distribution. This argument was given to Duncan Campbell when he made
enquiries about the system in the early 1980s. But the General Post Office could
equally well have used coaxial cables for television purposes. The first and second
London – Birmingham coaxial cables had both been designed with television
in mind and parts of the second L-BM cable are still used to carry television
programmes. Whilst microwave links have given extra capacity, television alone
would not have provided an overwhelming argument for establishing new microwave
links.

The POEEJ article gave an artist’s impression of the base stations for
the radio links –

We should not get over-excited about the use of the word “backbone”
in this early article. As many people have pointed out “backbone”
is a common term in communications technology to simply mean a central carrying
system, there are references from as early as 1909 to “backbone trunk telephone
circuits”. We are however concerned with a specific system which was officially
referred to as backbone with a capital “B”.

Further details of the system trickled out. For example a Ministry of Housing
& Local Government news release, from 15th March 1957 announced –

RADIO STATION TO BE BUILT IN CHILTERN VILLAGE: GOVERNMENT DECISION. The Government
have agreed to the siting of a Post Office radio station on land to the west of
the London-Fishguard road (A.40) ... near Stokenchurch, Buckinghamshire. [material
omitted] The station is required by the Post Office primarily for the purpose
of national defence but it will also have civil uses.

It seems odd that this and other public reports from planning enquiries openly
refer to a facility with an important defence function given that this was at
the height of the Cold War and only 6 years before the Spies for Peace caused
uproar by revealing the existence of the RSGs. At the time the government said
that the existence and siting of the RSGs was not secret but their functions were.
But the defence function of the new microwave system was openly made public.

Some of the Backbone sites were the subject of planning enquiries and luckily
for us these give us some further hints. For example in January 1961 The Times
announced -

The PO, Ministry of Works and Bucks CC were criticized by the Director-General
of the Nature Conservancy at the public enquiry over a proposed radio station
site in the Chilterns, which ended at High Wycombe yesterday. [much omitted] Mr
J Lawrence, appearing for the Postmaster-General, said the radio station would
be essential to Britain's defence policy. It would be a key point linking a chain
of radio stations in a national network of communications which would be vital
in time of attack, when normal landline communications might be destroyed.

So there were a few hints about what the system was for but these did not attract
a wide audience. We had to wait until records were released by the National Archives
to confirm some of what Laurie and Campbell had suggested and to fill in some gaps.

National Archives files
show that the plans for national defence communications in the early years of
the Cold War were as grandiose as they were financially impractical and they went
beyond Backbone. In 1956 the Official Committee (of civil servants) on Civil Defence
suggested that landline communications were vital to –

The air defence of the UK, particularly to link ROTOR
(GCI) sites to the Air Defence Operations Centre

The nuclear bombing retaliatory effort

Control of naval operations

Control of civil and military home defence forces, particularly with the Seat
of Government

The linking up to Central Government and Fighting Services headquarters of
long distance overseas communications

The 1956 paper said that these requirements could not be met by the existing
cable system for telephones and, more importantly telegraph because the long-distance
cable network went through cities and would be disrupted by an attack. It went
onto say that Post Office plans to protect wire communications were based firstly
on using a number of secondary cables, the “skeleton cable network”,
supplemented by backbone radio links and “radio stand by to line links”.

Here we have the 3 elements of the strategic network developed in the 1950s
to provide a survivable communications system initially during the expected prolonged
war involving atomic weapons and then from the mid-1950s when the strategy changed
during and after a very short one involving hydrogen bombs when the post-attack
aim would be simply to survive -

1. The skeleton cable network

This was to consist of a multiplicity of cables up and down the country which
did not pass through the largest towns. This was a development of plans from the
very early 1950s which aimed to protect communications by constructing -

Deep level accommodation for a “central unit of trunk service equipment
in London” and in 5 “very important industrial towns” with at
least one deep level cable tunnel from each to a point outside the target area.

Strengthened surface buildings in less important towns

Some dispersed buildings for switchboards in the cities and towns in 1. and
2.

Ring cables to bypass certain large towns.

The “deep level accommodation” resulted in the underground exchanges
in London, Manchester
and Birmingham which were all started around 1951(although Kingsway
In London was originally planned to be completed in 1949) and completed some 3
years later. Similar exchanges for Liverpool, Glasgow and Leeds were contemplated
but along with at least half of the other schemes mentioned below were never started
due to lack of money. London was also to have a scheme to protect transmission
equipment for central government and the FEDERAL exchange which was to be built
alongside the mysterious PIRATE scheme for underground protected accommodation
somewhere around or under Whitehall.

London would have a carrier ring main bypassing the capital some 30 –
60 miles from its centre. Other ring mains were considered for Birmingham, Manchester,
Glasgow, Bristol, Leeds, Liverpool, Derby and Newcastle.

Other towns such as Chester, Nottingham and Swansea would have “zone
schemes” which may have been schemes to disperse the central exchanges whilst
other places such as Plymouth and Belfast would be included in the protected buildings
schemes.

2. Backbone radio links

The 1956 paper said that the cable network could only provide a skeleton service
and would in any case take many years to complete and would therefore need to
be supplemented by the Backbone radio link [nb the report did use a capital “B”].
Backbone would consist of 14 radio stations each situated at least 10 miles from
a likely target running south to north up the country with spurs to Grantham and
Shrewsbury. The station buildings would consist of a tower for the aerials surrounded
at the base by a windowless, protected structure to house apparatus and staff
and provide protection against blast and fall-out. This confirms the details of
the sketch from the POEEJ article but it seems that in practice none of the stations
were built with any blast proof accommodation. The perspex shrouds shown in that
sketch were also not included in final constructions.

The report also confirms the POEEJ article when it said that the scheme would
provide 4 working broadband channels and 2 standbys. Each working channel would
have capacity for up to 600 circuits and 2 would be available for defence circuits
whilst the other 2 would be used to meet peacetime telephone trunk and TV developments.

The Backbone stations would form a high capacity network literally acting as
a backbone for line-based communications. Cables from public, defence and other
networks would connect to the stations which acted as terminals or nodes in the
network. The messages would then be routed along the network to the appropriate
receiving terminal where it would be directed back into the cable network. Originally
co-axial cables were used to give the required bandwidth although today fibre
optic cables would usually be used. Other stations in the network would act simply
as relays passing signals received onto the next station. Some stations are now
used by several services and will act as both terminals and relays. Most stations
would work automatically and be unmanned.

3. Radio standby-to-line

Even with Backbone many defence service private wires were still provided entirely
by cable. The purpose of the radio standby-to-line scheme was to provide alternative
channels of communications to cable, which although they might not go through
vulnerable cities still depended on numerous vulnerable repeater stations. It
would also be easier to protect a relatively small number of radio relay stations
so the idea was developed of a series of radio links from the Backbone stations
to military stations. Each link would carry 25 – 150 private wires. The
1956 plan shows radio standby-to-line routes connecting 5 ROTOR
Sector Operations Centres (SOCs) into Backbone sites. The Barnton
Quarry SOC in Edinburgh is not included but perhaps it would be linked to
the northern extremity of Backbone at Kirk o’ Shotts. One very interesting
link would have gone from West Malling [Fairseat] to Kelvedon
Hatch and then to connect to the original southern end of Backbone at Tring,
which was later replaced by Stokenchurch. Another route then went west from Tring
to Box which would serve the ROTOR SOC as well
as Admiralty establishments in Bath, the army switching centre at Boddington [Cheltenham]
and various other radio and radar sites in the south west. This route from West
Malling to Box may be the origin of the idea of a western Backbone route. Other
standby - to - line stations would link the ROTOR
sites at Ayr [Gailes], Boulmer and
Sneaton Snook to Backbone.

The 1956 report included a map of the proposed system –

Map: Backbone
as proposed in 1956

Photo: Coalville

Returning to Backbone, a lot of the PRO
information comes, perhaps surprisingly, from Countryside
Commission records. They show that by 1956 the plan was for a chain of 11
sites running south - north through the centre of England called radio relay stations,
radio beam stations or radio stations. The sites would be at Stokenchurch, Charwelton,
Coalville( Leics), Pye Green (Cannock, Staffs), Sutton Common (Macclesfield, Cheshire),
Saddleworth, Hunters Stones (Harrogate), Azeley Tower (Ripon), Richmond, Muggleswick
Common (Stanhope) to Bewcastle Fells (or Cold Fell) near Carlisle.

Three further towers were quickly added at Lockerbie (Dumfries), Lowther Hill
(Dumfries) and Kirk o’ Shotts (Lanarkshire) to take the chain into Scotland.
The sites were to be a maximum of 35 miles apart on a line-of-sight basis.

This initial plan had to be modified for various reasons but by 1959 the sites
for the Backbone chain had been more or less finalised. The Tring site was now
to be at Stokenchurch several miles to the south although the exact location was
not resolved until 1960. This was considered to be the key site where to quote
a 1960 report “the North, West, South and East routes come together and
where the radio route can be readily extended into London without requiring additional
stations and where it can be connected to existing cable routes.”. Charwelton
would use an existing GPO site while a new site officially called Coalville (although
it is nearer the village of Copt Oak) would be shared at with Leicestershire County
Council who were already using it. New sites would be needed at Pye Green and
Sutton Common and negotiations to buy them were at an advanced stage. It proved
difficult to acquire a site at Saddleworth and an existing site at nearby Windy
Hill was adopted.

The Hunters Stones site met with considerable opposition from
the Society for the Protection of Rural England (SPRE) but they eventually agreed
that if a site must be chosen in the general area the GPO’s preferred option
was acceptable.

In a letter written in April 1960 the GPO said “We now need this station
urgently to meet a civil telephony requirement as well as the defence requirement…Expansion
of the trunk telephone network between Manchester and Newcastle will depend on
the early provision of the new station and Hunters Stones has to link up with
the other existing PO radio stations”.

Assuming this letter, which was not classified, is correct and taking it at
face value it is very interesting. Firstly, it suggests that civilian needs were
important; secondly it may suggest that the siting of the Hunters Stones station
was by this time fixed by the needs to link it to other stations and thirdly it
argues against Duncan Campbell’s original suggestion that the Hunters Stones
tower was sited to serve the Menwith Hill sigint station. In fact Menwith Hill
did not become operational until 1959 and was not taken over by the National
Security Agency until 1966.

Certainly, high capacity links were established between Menwith Hill and the
Hunters Stones tower by 1975 but it now seems likely that the proximity of the
sites is co-incidental rather than planned.

Photo: Corbys Crag 1975

By 1959 the GPO were proposing to replace both the Azerley and Richmond Hill
sites with one at Arncliffe Wood. SPRE objected but lost. They also objected to
the site at Muggleswick for which negotiations were already under way.

It appears that by 1959 the stations beyond Muggleswick had been reconsidered.
Cold Fell was abandoned and replaced by an existing site at Corbys Crag where
the local planning authority had gained the false impression that an existing
70 foot TV mast would be replaced by the new 220 foot mast “required for
Service Department communications systems…”. Corbys Crag was the last
English site to be acquired being finalised by November 1961. Unfortunately, the
available records give no information about the northward march of Backbone into
Scotland.

There is no suggestion in these records that Backbone was meant to go anywhere
other than the south – north route with the east – west extensions
across the midlands where Shrewsbury appears to correspond with “War
Plan UK’s” Albrighton. There are however hints of what happened
after say 1960. One of the oddities about the history of Backbone, and it is tempting
to say that this could only happen in Britain is that a project apparently needed
for national defence at the height of the Cold War could be delayed by what would
now be called the environmental lobby notably the SPRE, the National
Trust, the National Parks Commission and, perhaps most surprisingly, the Fine
Arts Commission. This was because many of the sites which had to be away from
built up areas and on high ground were in what we would now call environmentally
sensitive areas. These bodies had to be consulted and the delays this entailed
together with those self-imposed by the GPO and the lack of funds from central
government seem to argue against the Backbone being particularly important. However,
the planning enquiries which these bodies required give us some important insights
into the scheme.

Photo: Five Ways

This original Backbone scheme plan was conceived in 1954 apparently
primarily for defence and plans were actively being made by 1956 but the plan
ran into various problems with equipment design and site acquisition. Following
the Strath
Report there was also a reappraisal of the need for such strategic communications
systems.

Now the planners assumed that the next war would be over very quickly and there
was no need to provide for “due functioning” so the need for these
survivable communications systems diminished.

But more importantly, and as usual for civil defence there was no money to
implement the plans and even in 1957 the Official committee on Civil Defence was
saying that there was only funds to complete half of Backbone but by then the
plans had already been deferred so that it was planned that the southern part
of Backbone would not be complete until 1962 and the northern part not until 1964.

It appears that around 1960 many more microwave stations were planned with
perhaps the most well known being the towers in the centres of London (started
1961), Birmingham (started 1963) and Manchester. These towers together with ones
in Bristol and Leeds are in direct contradiction of the original idea that Backbone
would provide a route by-passing the major cities which might be attacked in war
and suggest that the new stations had different priorities.

One of these later “post-Backbone” stations at Wotton under Edge
attracted a lot of attention. In December 1962 a public enquiry was held into
this proposed site which gives us a lot of information about official thinking.
The GPO witness to the enquiry said that the GPO was responsible for communications
up to and after attack and therefore its services must be provided in advance.
Nearly all the long distance circuits were underground and passed through densely
populated areas and might be damaged by an attack. Radio stations would be less
likely to suffer damage and consequently as a safeguard against attack the PO
supplemented cable by a radio-relay network which must 1. avoid population centres
and 2. be survivable. He added that the primary need was for defence and the Wotton
tower was needed to link to 4 adjacent ones. A map provided did not specify these
4 sites but it is noteable that it has an 'arrow pointing exactly towards the
Five Ways mast at Corsham'. The
mast here was built in the early 1960s and probably only carried only one horn.
Unusually, if not uniquely the mast was truncated in the late 1980s and it is
now only half its original height. Corsham is the base of the RAF’s main
switching and signal centre and since the 1960s the home of the Defence Communications
Network. It was also the site of the central government emergency war headquarters
where by the early 1960s the communications were being installed.

The final report of the government inspector heading the Wotton enquiry summed
up the GPO case and gave some more revealing detail. He said “An extensive
network of radio links has already been established in the UK for relaying TV
signals for the BBC and ITA and this network is being extended to provide essential
defence telephonic and telegraphic circuits. It is also to meet growing demands
for public trunk telephone circuits and additional TV relaying facilities amounting
to several thousand phone circuits and TV channels over the next 5 to 10 years.
The station which the PO is to establish would be the key radio relay station
in this network serving routes to the west, south west, south and east for extension
to London.” This paragraph brings out the idea that the station was needed
for civilian telephone and TV use but it is important to note that these civilian
needs are not really needed for at least 5 years. The “essential defence”
need obviously exists. This idea is confirmed in later paragraphs where the Inspector
said “It is the responsibility of the PO to plan the telephone and telegraph
network to the best advantage should hostilities break out. With this in mind
and in consultation with civil and service departments it agreed to provide an
alternative radio-relay system network to the established cable network…this
policy is in accordance with the White Paper on Defence of 1955.

In this connection the station must be suitably
positioned to connect with existing stations in the main west-bound route which
has been positioned to minimise the probability of interruption during war-time.

The station must also be located where the radio routes can be extended to
London by means of a route to the east using existing radio stations…”
He later added “…the primary need for a radio station near Wotton-under-Edge
is to maintain essential defence telephone and telegraph communications…”.

The enquiry in fact considered 2 sites a few miles apart and it seems to have
been important that they were on the right contour (ie height above sea level).The
Inspector recommended that permission be granted which in September 1963 it was.

Photo: Sutton Common 1976

Another PRO file mentions stations at Fairseat and Flimwell being acquired
in 1962. These appear on the map in “War
Plan UK” as non-Backbone microwave link stations but Fairseat may correspond
to the West Malling “radio standby to line” station which appears
on the 1956 Backbone map. Public enquiries into the Fairseat and Flimwell sites
in 1963 refer to a defence need as did the one into the Butser Hill site near
Portsmouth. Here the main requirement was said to be for the GPO “…as
part of the countrywide telecommunications pattern for telephone services, TV
and defence purposes to which they are committed.” The impression the available,
albeit limited information, gives is that the new burst of stations built in the
early 1960s was primarily for civilian purposes but it would have a secondary
and probably incidental military use. But given the large numbers of these new
stations and their cost it seems very unlikely that defence needs were a principal
driving force because there was never any money available in the home defence
budgets to pay for them. It is tempting to speculate that defence needs were cited
at public enquiries on the grounds that this would be treated more sympathetically
than commercial needs. By 1965 the GPO microwave network covered some 130 stations
centred on the new GPO Tower in London which itself could handle 150000 connections
and 40 TV channels – a far cry from the capacity of the original Backbone
stations.

One apparent oddity of the stations is that while the majority are steel lattice
masts a few are elegant “pencil type mast” structures made of concrete
as shown in the original POEEJ article. This has lead to considerable speculation
as to the reasons for the different types. The answer however seems to be quite
simple. In 1962 the GPO wrote “We have designed a concrete tower for those
few stations where technically a lattice tower would not be suitable. Our plans
for this chain of stations include only 6 such towers…” Evidence to
the Wotton enquiry says that in 1961 the Royal Fine Arts Commission approved a
design similar to Wotton (ie a pencil tower) for Sutton Common, Pye Green, Charwelton
and Chiltern. The missing sixth tower was Morborne Hill, near Peterborough. Further
evidence was provided by the GPO witness who said that the general construction
of the Wotton tower would be of reinforced concrete with unwrought timber shutters
to the external face to give a pleasing appearance to the finished concrete. He
said that a similar design has been found aesthetically acceptable by the Royal
Fine Arts Commission and added, significantly, that the concrete and the microwave
dishes could be painted to blend in with the countryside. So the clue appears
to be in the siting of the concrete towers – they are all in environmentally
sensitive areas. The GPO wanted to use steel masts because they had a greater
load carrying capacity but the concrete ones are less of an eyesore and more acceptable
to the environmental lobby groups. Apart from the 6 rural Backbone stations the
only other concrete towers are post-Backbone ones in cities – London, Birmingham,
Manchester, Leeds and Bristol, or in the case of Tolsford Hill high on the North
Downs near Folkestone. They would all be very visible to many people and this
adds to the impression that the difference structures were dictated simply by
appearance with aesthetics overruling function.

Photo's: Stokenchurch – as
shown in a 1961 press release after criticism of its visual impact and (below)
as built (although originally horns were fitted rather than dishes.

Although Backbone is frequently mentioned in PRO files on home defence in the
late 1950s it is hardly mentioned at all in the 1960s. It seems that the original
Backbone stations became absorbed into a much larger microwave network and reports
speak of “completion of the system which began with Backbone” and
“stations supplementing Backbone”. Files which give details of pre-and
post-strike communications from the end of the 1960s do not mention it at all.